Observations of internal wave packets propagating along-shelf in northern Monterey Bay

Abstract

[1] Internal waves of depression were observed propagating along-shelf and into northern Monterey Bay, California (CA) on the inner shelf. These waves had amplitudes approximately equal to the thermocline depth (∼4 m), and were unstable to shear and mix the thermocline. Isopycnal gradient spectra showed that the wave packets lead to an elevated mean dissipation rate of " = 2.63 × 10 −5 m 3 s −2 for up to 2 hours after wave passage. The proximity to the surface created strong surface convergences that can actively transport buoyant material, such as plankton, back into the bay. The wave packets were observed regularly over the upwelling season across multiple years suggesting they may have large effects on the documented spatial variation of phytoplankton and larvae on the inner shelf. The timing of the waves suggests they are not formed by tides interacting with bathymetry, but are generated by buoyant plume propagation.

Mapping ocean outfall plumes and their mixing using autonomous underwater vehicles

“…These variations are indicative of large amplitude internal waves propagating through the study area [ Phillips , 1977; Nash and Moum , 2005; Stanton and Ostrovsky , 1998; Moum et al , 2007; Helfrich and Melville , 2006]. These waves have a trailing turbulent field that mixes and thickens the pycnocline [ Woodson et al , 2011].…”

Submarine groundwater discharge in Northern Monterey Bay, California: Evaluation by mixing and mass balance models

“…The near shore terminus of SB is near the mouth of Monterey Bay and allows easy access for advected upwelling water from Año Nuevo to the near shore. Almost the entire SA transect overlies the Monterey Canyon, which allows for advection of deep water to the surface of Monterey Bay year round (Shea and Broenkow, 1982;Woodson et al, 2011).…”

Scale-Dependent Dispersion within the Stratified Interior on the Shelf of Northern Monterey Bay

“…The lateral axis of the plume is therefore aligned with the cross-shelf direction. T-S plots (not shown) from the top-and bottom-mounted CTDs at C0 indicate that density variations were dominated by temperature variations, behavior that is expected during the summer upwelling months in Monterey Bay (Woodson et al 2011). Therefore, in what follows we consider the thermocline and pycnocline to be synonymous and give preference to the former with the use of the thermistor records.…”

“…The stratification supports internal waves that are observed to propagate predominantly onshelf (median heading of 3508) at periods within a range of 12-15 min. These high frequency internal waves may be associated with the degeneration of the semidiurnal internal tide (Petruncio et al 1998) or with wind forcing of the warm surface layer (Woodson et al 2011) and are therefore not generated at the site. The variance-preserving spectrum of a midwater column temperature record supports this internal wave characterization given an increase of temperature variance between 10 0 and 10 1 cph that does not exist in the spectra for surface and bottom temperature time series (Fig.…”

“…Within the stratified coastal shelf waters of Monterey Bay, California, important transport and mixing mechanisms include wind-driven diurnal upwelling and internal waves and bores (Drake et al 2005;Petruncio et al 1998;Woodson et al 2007;Walter et al 2012); these reflect the complex interaction of regional-scale forcing on local coastal flows (C. B. Woodson and D. A. Fong 2013, unpublished manuscript).…”